This resubmission of a Revision (formerly Competing Supplementary) application seeks support to augment the currently funded POI grant POI HD 025995, "Stimulus Control in Mental Retardation." Three of the currently funded projects are evaluating response to visual stimuli in individuals with intellectual disabilities: Projects 1&2 study stimulus structure variables and variation in stimulus features such as color and form that may be important in promoting desirable forms of stimulus control in functional academics and augmentative/alternative communication (AAC), respectively. Project 3 studies stimulus control processes in the detection of facial expression and emotion by persons from various disability groups. The proposed Project 5 will expand the scope of the current research program to address the problem of stimulus over-selectivity as it may impact stimulus control in functional academics, augmentative/alternative communication, and face processing. Overselectivity refers to maladaptive narrow attending that is a common learning problem in children with intellectual disabilities. Overselectivity is often associated with autism spectrum disorders (ASD), but the research foundation for this relation is based largely on simple discrimination learning procedures that fail to capture the complex relational learning aspects of special-education curricula. Research at the Shriver Center and elsewhere has produced methodologies to study overselectivity in contexts that model teaching situations. We have also developed an approach toward remediation that incorporates differential observing response (DOR) procedures;this approach can eliminate the problem by corrective therapy for some individuals and by behavioral prosthesis for others. Project 5 proposes a formal comparison of stimulus overselectivity in the four study populations of the ongoing program project: MA- and CA-matched children with ASD, Down syndrome, &intellectual disabilities of mixed/unknown etiology;and MA-matched typically developing children. Stimulus sets of clinical/educational interest will parallel those of the existing POI projects (AAC icons, photos of faces). We will determine whether an ASD diagnosis is related to (1) increased prevalence or severity of overselective stimulus control;and (2) the effectiveness, durability, and net gain resulting from intervention with DOR procedures and remedial training. We also propose a series of applied studies to examine generalization and durability of DOR interventions in special-education classrooms. The results will enhance the applications potential of the other projects and contribute to a better characterization of the learning problems associated with the study populations.